CHAP. VII. COMPARED WITH THE DEEPER PARTS. 123 is obliged to extend the incision, it is properly considered an awkwardness; not only because it proves that he has miscalculated what was necessary to the correct performance of his operation, but because the patient, bearing courageously the deeper incisions, cannot sustain the renewed cutting of the skin, without giving token of severe pain. The fact of the exquisite sensibility of the surface, as compared with the deeper parts, being thus ascertained by daily experience, we cannot mistake the intention: that it is to make the skin the safeguard to the delicate textures within, by forcing us to avoid what will injure the surface. And it does afford a more effectual defence, than if our bodies were clad with the hide of the rhinoceros. The greater the consideration we give to this subject, the more convincing will be the proofs that the painful sensibility. of the skin is a benevolent provision; that it makes us alive to injuries, which would otherwise bruise and destroy the internal vital organs. In pursuing the inquiry, we learn with much interest, that when bones, cartilages of the joints, or the membranes and ligaments which cover them, are exposed-they may be cut, pricked, or even burned, without the patient, or the animal, suffering the slightest pain. We have arrived at the full comprehension of this subject slowly; disagreeable experiments have been made: but the following is as interesting as it was innocently performed. A man, who had his finger torn off, so as to be connected by the tendon only, came to a pupil of Dr Hunter: “I shall now see," he said, "whether this man has any sensibility in the tendon." He laid a cord along the finger, and blindfolding the patient, cut across the tendon. "Tell me," he asked, "what I have cut?" "Why you have cut across the cord, to be sure," was the answer. At first, these facts would appear to prove, beyond all question, that the structures enumerated are devoid of sensation. After witnessing such remarkable instances of absence of pain, who could come to any other conclusion? But if we adopt the true, philosophical, and, I may say, religious view of the subject, and consider that pain is not conferred as an evil, but, on the contrary, for benevolent and important purposes, we perceive that the subject requires further elucidation. In the first place, it is obvious, that if a sensibility like that of the skin had been bestowed upon these internal parts, it must have remained unexercised. Had the bones, cartilages, ligaments, or tendons been rendered sensible to pricking or burning, they would have possessed a quality never to be useful; since, without previous warning received through the skin, no such injuries as these could reach them. But further, allowing pain to be a benevolent provision which admonishes us to avoid such violence as would affect the functions of parts, we may yet inquire whether certain other injuries may not reach these internal structures, without warning from the skin. Now, of this there can be no doubt; the textures around the joints are subject to sprain, rupture, and shocks, while the skin may not be at all implicated in the accident. Accordingly, notwithstanding the apparent demonstration by experiment that these internal parts are devoid of sensibility, it is evident that they must possess an appropriate kind of feeling, or it would imply an imperfection. Every day's observation shows that such is the case: for we find that the cartilages, ligaments, and tendons, which may be pricked, cut, or burned, without exhibition of pain, are acutely sensible to concussion, stretching, or laceration. Is it not remarkable that men, the luminaries of their profession, should have held that these parts were insensible ; and yet that they should have been in daily attendance upon persons suffering from sprained ankle; where the structures injured are the very ones enumerated, and where the pain, felt at the instant of the sprain, is excessive ? How consistent, then, and beautiful is the distribution of this property of life! The sensibility to pain varies with the function of the part. The skin is alive to every possible injurious impression likely to be made upon it; but had the same kind and degree of sensibility been universal,-had the membranes between the bones of our great joints, or the ligaments which knit the bones, or the tendons of the muscles, been sensible in the same manner and degree as the skin, or surface of the eye, we should have been racked with pain in the common movements of the body—the mere weight of one bone on another, or motion of a limb, would have been attended with suffering as acute as that of a man who should attempt to walk in a violent attack of rheumatism. On the other hand, had the deeper struc tures possessed no sensibility, we should have been without a guide to our exertions. The internal parts do possess sensibility; but it is limited to warning us of those kinds of injury alone which may possibly reach so deeply. It teaches us what we can do with impunity; if we leap from too great a height, or carry too heavy a burden, or attempt to interrupt a body whose impetus is too powerful, we are admonished of the danger as effectually by this internal sensibility, as of the approach of a sharp point, or a hot iron, to the skin. Accordingly, pain is not given here superfluously: the safe exercise and enjoyment of every part is permitted without alloy: the excess only is restrained. In continuation of this view of the benevolent object for which pain is awarded, I may be excused for stating the argument as I have delivered it in my lectures : "Without meaning to impute inattention or restlessness, I may request you to observe how every one occasionally changes his position, and shifts the pressure of the weight of his body. Were you constrained to keep in one position during the whole hour, you would rise stiff and lame. The sensibility of the skin here guides you to do that which, if neglected, might be followed even by death of the part. When a patient is affected with paralysis of the lower half of the body, we give especial directions to the nurse and attendants to change the position of his limbs at short intervals, to place pillows under his loins and hams, and to shift them often. If these precautions be omitted, you know the consequence to be inflammation of the integument where the pressure is directed; and from that come fever, local irritation, and death. "Thus you perceive that, without disturbing your train of thought, the natural sensibility of the skin induces you to shift the body, so as to permit the free circulation of the blood in the minute vessels: and when this sensibility is lost, the utmost attention of friends, and the watchfulness of the nurse, are but poor substitutes for the protection which nature is continually affording. If you thus suffer, lying on a soft bed, how could you encounter the rubs and shocks incident to an active life, if deprived of the sense of pain in the skin? You must acknowledge that the sensibility of the integuments is as much a protection to the frame generally, as that of the eyelids is to the eyes; and the reflection suggests a motive for gratitude which probably you never thought of before." Sensibility of the hand to the varieties of temperature is a different endowment from that of touch. This property is seated in the skin, and is, consequently, limited to the exterior surface of the body. The internal parts being of uniform temperature, it would have been superfluous to bestow it upon them. As we are surrounded by an atmosphere the temperature of which is continually varying, its extremes might cause the destruction of our frame; and as we must suit our exertions or contrivances to sustain life against such vicissitudes, the possession of this peculiar sensibility affords another proof of a foreknowledge of our condition. To illustrate the evils which might befall us were it not for this sensibility, we might recur to our former example. The paralytic, having no sense of the extremes of temperature is frequently severely burned; or his extremities may be mortified through cold. A man, who had lost this sense in his right hand, but retained muscular power, lifted the cover of a pan, which from falling into the fire was burning hot, and deliberately replaced it, without being conscious of the heat; the effect, however, was that the skin of the palm and fingers was destroyed. The same man had a continual sensation of coldness in the affected arm, which actual cold did not aggravate, nor heat in any degree assuage. * Sensibility to heat, inasmuch as it is capable of becoming a painful sensation, is not only a safeguard, but a never-failing excitement to activity, and a continual source of enjoyment. Cold braces and animates to exertion, whilst the warmth which is pleasant to us, is genial to all the operations of the animal economy. And here we may remark an adaptation of the living property, very different from a physical influence. Heat is uniform in its effect on dead matter; science informs us that warmth *There are certain morbid conditions of sensation when cold bodies feel intensely hot.-Dr Abercrombie's Inquiry into the Intellectual Powers. It is a curious illustration of the powers of the cutaneous nerves to receive impressions of the varieties of temperature, that when one is affected by disease anywhere in its | course, the sensation of burning may accompany the pain; and the patient will refer the sense of heat to that part of the skin to which the extreme branches of the nerve are distributed. By a burning sensation in the sole of the foot, the surgeon may be directed to disease seated in the centre of the thigh. and cold are only relative degrees of caloric. But the sensation varies, as heat is given to, or abstracted from, the living body. To the skin, cold and heat are distinct sensations; and without such contrast, we should not continue to enjoy the sense. For in the nervous system it holds universally, that variety, or contrast, is necessary to sensation; the finest organ of sense losing its property by the continuance of the same impression. It is by a comparison of cold and heat that we enjoy either condition. To contrast still more strongly the sensibility of the external surface with the endowments of the internal parts; and to show how very different from what is suggested by first experience the property sensibility generally is, and how admirably varied and accommodated it is to the functions, we shall add one other fact. The brain is insensible-that part of the brain which, if disturbed or diseased, takes away consciousness, is as insensible as the leather of our shoe! That the brain may be touched, or a portion of it cut off, without interrupting the patient in the sentence that he is uttering, is a surprising circumstance! Physiologists formerly inferred, from this fact, that the more important organ of the brain had not been reached. But that opinion arose from the notion that a nerve must necessarily be sensible; whereas, when we consider that different parts of the nervous system possess totally distinct endowments, and that some nerves, as I have elsewhere shown, though exquisitely alive to their proper office, are insensible to touch and incapable of giving pain, we have no just reason to conclude that the brain should be sensible, or exhibit the property of a nerve of the skin. Reason on it as we may, the fact is so; the brain, through which every impression must be conveyed before it is perceived, is itself insensible. This informs us that sensibility is not a necessary attendant on the delicate texture of a living part, but that it must have an appropriate organ, and that it is an especial provision.* To satisfy my reader on this interesting subject, I shall contrast two organs, one external and exposed, and the other internal and carefully excluded from injury. The eye, consisting of its proper nerve of vision, and its trans * See the Sensibility of the Retina, "Additional Illustrations." |